Forced convection surface evaporator



y 1970 J. CHAMBERS 3,509,932

FORCED CONVECTION SURFACE EVAPORATOR Filed Nov. 16, 1967 5 Sheets-Sheet 2 IN VE N 70/? JOHN CHA MBERS I MWZo/ M,

ATTORNEYS y 70 J. CHAMBERS 3,509,932

FORCED CONVECTION SURFACE 'EVAPORATOR Filed Nov. 16, 1967 5 Sheets-Sheet 1 1 r uouao Al 7 27 FIG. I 6 l :28 24c:

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//v VE/VTOR JOHN CHAMBERS w, M, M

Waolflm ATTORNEYS May 5, 1970 J. CHAMBERS FORCED CONVECTION SURFACE EVAPORATOR 5 Sheets-Sheet 5 Filed NOV. 16, 1967 IN VEN TOR JOHN CHAMBERS AT 7' ORNE Y8 May 5, 1970 J. CHAMBERS FORCED CONVECTION SURFACE EVAPORATOR Filed Nov. 16, 1967 5 Sheets-Sheet 4.

IN VE/V 70/? JOHN CHA M8595 M 2264, Wmm

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A T TOR/VEYS United States Patent Int. Cl. B01d N16 US. Cl. 1592 9 Claims ABSTRACT OF THE DISCLOSURE A forced convection surface evaporator comprises means for elfecting a flow of heated liquid to be evaporated, means for initiating evaporation of the liquid by varying the pressure of the liquid in a direction transverse to the direction of flow and also in the direction of flow, said initiating means being capable of reducing the pressure of the liquid in the direction of flow to its vaporizing pressure. Means for maintaining the evaporating of the liquid thus initiated includes means for imparting turbulence to the liquid and thereby effecting a transfer of heat to the surface of the liquid. Also included are means for controlling the rate of evaporation from the surface of the liquid so as to permit expansion of the vapor while preventing nucleate boiling within the body of the liquid.

This application is a continuation-in-part of application No. 528,520 filed Feb. 18, 1966 now abandoned.

This invention relates to methods of and apparatus for separating one or more vapors from a liquid or mixture of liquids or from a mixture of liquids and vapors or gases. The invention can be used in the purification of liquids and in the fractional separation of a plurality of substances having different vapor pressures from a mixture of such substances. The apparatus and methods described herein may also be used to concentrate solutions by separating the solvent from the solution and in other applications.

In the devices of the present invention vapor-liquid separation is accomplished in a continuous manner by forced convection surface evaporation. The surface evaporation is started by the substantially simultaneous effects of centrifugal force and reduction of the liquid pressure below that of the vapor pressure of one or more fractions thereof. The surface evaporation is continued after it is started by keeping the liquid turbulent and by controlling the rate of evaporation from the liquid surface in relation to the turbulency and thickness of the body of liquid flowing through the evaporator.

After the required degree of evaporation has been reached, the vapors are removed from the structure in which the evaporation occurs through one or more offtakes, depending upon the number of fractions being separated. When only one fraction is being separated, only one offtake is needed. Where more than one constituent is being removed from the mixture there may be a plurality of offtakes for the separated vapors. Such ofitakes are preferably staggered along the length of the nozzle (and located at diiferent distances from the inner wall of the 3,509,932 Patented May 5, 1970 nozzle in the case of a curved nozzle) to produce a clean separation of the different fractions.

The present invention is highly efiicient and is especially applicable to the separation of fresh Water from sea water, a field in which a large number of processes are under current investigation for the production of fresh water for use in industry and for drinking purposes. Other uses, by way of example are: .(a) forming and separating a vapor from a parent liquid of the same chemical composition; (b) forming and separating a vapor from a liquid containing other chemical compositions in addition to the chemical composition of the vapor; (C) forming and separating vapors or gases of dilferent chemical compositions from a liquid containing the same chemical compositions as the vapors; and (d) forming and separating vapors of different chemical compositions from a liquid containing the same chemical compositions as the vapors as well as other chemical compositions. In any of these cases the primary purpose may be the recovery of the separated vapor or the concentration of constituents in the original liquid or liquid mixture.

From the foregoing it will be apparent that it is the primary object of the invention to provide novel methods of and apparatus for separating one or more liquids in the form of vapor from a liquid or a mixture of liquids.

Other objects, further advantages, and other important features will become apparent from the appended claims and as the ensuing description and detailed discussion proceeds in connection with the annexed drawings, wherein:

FIG. 1 is a section through one form of evaporator constructed in accord with the principles of the present invention;

FIG. 2 is a similar view of a second embodiment of the invention;

FIG. 3 is a view similar to FIGURE 1 of a third form of the invention;

FIG. 4 is a vertical section through the center of an evaporator of the centrifugal or curved nozzle type constructed in accord with the principles of the present invention;

FIG. 5 is a view similar to FIGURE 4 of another centrifugal type evaporator which has diverging diffuser sections in the discharge conduits or olftakes;

'FIGS. 6 and 7 are views similar to FIGS. 4 and 5, illustrating modifications of the evaporators shown in the latter;

FIG. '8 is a vertical section through a curved nozzle evaporator for a mixture of liquids having different vapor pressures and provided with a plurality of oiftake passageways for different gases or vapors;

FIG. 9 is a view similar to FIG. 8 of a centrifugal evaporator having diverging diffuser sections in the discharge conduits of the evaporator;

FIG. 10 is a section through a forced convection surface evaporator in accordance with the present invention in which a reduction in static pressure is effected by introducing the liquid to be evaporated tangentially into the evaporator; and

FIG. 11 is a section through the evaporator of FIG. 10, taken substantially along line 11-1 1 of the latter figure.

In the evaporators of the present invention four prerequisites are combined to effect liquid separation in an 3 efiicient manner. Two of the operating prerequisites are necessary to start the surface evaporization, and the remaining two are necessary to continue the surface evaporization, and the remaining two are necessary to continue the surface evaporization after it has been started. The prerequisites for starting the evaporation are:

(1) A means for varying the static pressure of the liquid being evaporated in the plane normal to the axial flow of the liquid.

(2) A means for lowering the static pressure of the liquid to its boiling point in the axial flow direction.

The prerequisites for maintaining the surface evaporization after starting are:

(3) A means for keeping the liquid turbulent after surface evaporization has commenced.

(4) A means for controlling the rate of evaporization from the liquid surface in relation to the turbulency and thickness of the liquid.

With respect to the first of these four prerequisites, a centrifugal force can be and preferably is utilized in the present invention to vary the static pressure of the liquid in the plane normal to the axial flow. This centrifugal force can be imparted by a curved wall, by a sharply convergent nozzle section, which will cause a vena contracta and hence a centrifugal force, or by an orifice, which also causes a vena contracta. The centrifugal force can also be induced by swirling the liquid by spirally twisted guides before the water reaches the vaporizing pressure in the throat of the evaporator. Swirling can also be induced by introducing the water tangentially into the flow system upstream of a nozzle in order to make it swirl through the axial flow point where vaporization starts.

As far as the second of the above-mentioned prerequisites is concerned, there is only one way to lower the static pressure of the liquid to its vapor pressure in the axial flow direction to start the evaporization. This is to increase the liquid velocity through a converging nozzle entry section. This converging section can be gradual or abrupt like an orifice. However, if it is abrupt a vena contracta will be formed. This is advantageous since, as mentioned above, the vena contracta will also produce a centrifugal force, causing the first prerequisite to be fulfilled. If the converging section is gradual the centrifugal force necessary to start surface evaporation has to be induced by a swirl or by other means.

The third prerequisite is that turbulency be introduced into the liquid after evaporation has started. This is accomplished through the introduction of friction by providing a surface against which the liquid can rub. The degree of friction produced by this surface determines the turbulency, which is conventionally measured by Reynolds number.

The fourth prerequisite of the present invention is that the rate of evaporation be controlled. This is done by proper selection of the inclusive angle between the walls in the divergentsection of the evaporatonlt is preferable that this angle be as large as possible since the larger the angle is the faster the rate of evaporation per unit area of the liquid surface will be. Also, if the angle of the divergent section is too small choking will occur (a full expansion cannot be realized). However, there is a limit to the magnitude of this angle. Specifically, if the angle of the divergent section is too large the heat of the water will not be brought to the Water surface quickly enough 1 and the surface evaporization will break down and nucleate boiling will occur (vapor bubbles will form within the liquid). Nucleate boiling is undesirable since the whole mass of liquid and vapor is accelerated evenly, producing a problem of separating the vapor from the liquid. It is desirable to have two separate velocities-a high velocity for the vapor and a low velocity for the water.

1 The turbulency of the water delivers the heat in the water up to the surface of the water. In order to keep the surface evaporation operating a balance must be maintained between the rate of delivery of the heat in the water to the water surface and the rate of vaporization at the water surface.

Referring now to the drawing, FIGS. 1-3 illustrate embodiments of the invention in which the first two prerequisites (variation of static pressure in a plane normal to axial flow and the lowering of the static pressure of the liquid to its vapor pressure) are fulfilled by using an orifice (FIG. 2) and a sharply convergent nozzle section (FIGS. 1 and 3). In these figures the flow of liquid is from left to right through a reduced diameter or venturi section of a conduit, the liquid being discharged at the right and vapors being removed adjacent the venturi section.

Referring first to FIG. 1, an inlet conduit 23 to the evaporator, preferably circular in cross-section, has an internal cross-sectional area indicated by the diametric line A The conduit has an inwardly converging section 21 with a maximum diameter A and minimum diameter A and an outwardly diverging section 22. Conduit sections 21 and 22 meet at angle 0 at juncture 25. Converging section 21 and diverging section 22 are connected at their upstream and downstream ends respectively to a cylindrical section of liquid inlet conduit 23 and to a vapor outlet conduit 24.

An elongated, axially extending r-od 24a is mounted in the evaporator in any convenient fashion. This rod is employed to fulfill the third prerequisite of evaporators according to the present invention; i.e., to introduce turbulence into the liquid in order to transfer heat to the vapor-liquid interface and thereby keep the evaporation process going.

As shown in FIG. 1, rod 24a may be disposed in the conduit in such a manner that the axial centerlines of the rod and evaporator are substantially coincidental. This is not essential, however, and the rod may be disposed at one side of the passage through which it extends, if the circumstances surrounding a particular application of the invention so dictate.

In operation, using sea water as an example of a liquid to be evaporated and water vapor as the vapor to be separated, heated sea water enters the conduit 23 at a suitable temperature and velocity and passes through the converging section 21 and diverging section 22 of the evaporator. As it passes through the evaporator, the static pressure of the water in the transverse plane and that in the axial flow direction are decreased until part of the water flashes into steam, an annular bubble of vapor (indicated by the dotted line 26) being formed just downstream of juncture 2'5. Formation of the vapor is continued due to rod 24a which is surrounded by the vapor, as shown in FIG. 1 and by the diverging wall of evaporator section 22, which permit the vapor to expand and thereby eliminate choking, yet confine the vapor to a sufficiently small area to maintain surface evaporation and prevent nucleate boiling.

As suggested above, the angle of divergence which is preferably employed is the maximum which can be used without nucleate boiling since this will produce the maxi mum rate of surface evaporation. For any particular evaporator configuration and set of operating conditions this angle has to he generally determined by actual test 2 although it has been established that angles as large as are too large to prevent nucleate boiling.

To separate the annular bubble of vapor from the main stream of liquid passing through diverging section 22, a tube 27 is located coaxially within vapor outlet 24 with its open upstream end 28 extending into the space within the diverging section 22 where the annular bubble 26 exists. The vapor within the bubble 26 is removed through the annular space between the tube 27 and the vapor outlet 24, while the liquid is taken oif or removed through the central outlet tube 27. The annular space between 'F0r a particular configuration test data can be reduced to a plot of Reynolds number versus maximum included angle. Thereafter, the included angle for turbulence of specified magnitude 1n the divergent evaporator section can be readily ascertained.

tube 24 and tube 27 may be connected to a conventional low pressure vapor removal device such as a pump or condenser (not shown) to facilitate the vapor removal, if desired.

As discussed above, one of the requirements for proper operation of the evaporator just described is a sharp juncture between converging and diverging evaporator sections 21 and 22 at an angle 0 sufiiciently small to produce jet flow and a contraction of the stream of unevaporated liquid downstream from juncture 25. Formation of this vena contracta is necessary to provide two-phase expansion of the liquid being evaporated and clean separation of the liquid and vapor by insuring surface evaporation and confinement of the liquid to a stream which will flow into exit tube or conduit 2-7 and by providing suflicient area for the liquid to contract and form vapor apart from the unevaporated liquid downstream of juncture 25.

Also, unless a vena contracta is formed by the proper relative disposition of converging and diverging evaporator sections 21 and 22, there Will be no centrifugal force to start surface evaporation. Instead, bubbles will form within the liquid and the bubbles of vapor and stream of saturated unevaporated liquid at juncture 25 will have approximately the same velocity. Consequently, the vapor will choke the nozzle and will not expand to a significant extent; and there will not be a clear separation of the vapor and liquid downstream of juncture 25 as the vapor and liquid will tend to follow the same paths. This is at least in part due to the negligible velocity of the vapor and its intricate mixture of the unevaporated liquid.

As the angle 0 between converging and diverging evaporator sections 21 and 22 decreases (i.e., as the juncture between them becomes steeper or sharper), the contraction of the jet of unevaporated liquid increases. This is reflected in greater two-phase expansion and separation of the vapor and liquid phases through surface evaporation.

Maximum contraction is obtained in the evaporator 30 of FIG. 2 in which the juncture between the converging and diverging sections 21 and 22 of the evaporator previously described is replaced by the upstream and downstream sides 31 and 32 of a sharp edged orifice 33 in inlet conduit 34 so that the evaporator inlet or converging section has an inlet diameter of A and an outlet diameter of A and angle 0 is zero. This provides substantial two-phase expansion and clean separation of the liquid and vapor phases, the former flowing into liquid outlet conduit 33a and the latter into vapor offtake conduits 33b.

In the embodiment of FIG. 3, the liquid inlet 36 is a cylindrical tube similar to the inlets 23 and 34 of FIGS. 1 and 2, and its cross-sectional area is represented by the diametric line A as in the latter figures. In this embodiment the upper portion of the inlet 36 has a converging section 37 terminating at a neck or sharp juncture 38. The lower half of the inlet 36 is straight in this embodiment of the invention, and it terminates in a liquid outlet tube 39. In this case a bubble of vapor, indicated by dotted line 40, forms downstream of the neck or juncture 38; and the vapor is collected and removed by a conduit 41, which meets the liquid outlet tube 39 at an angle, the juncture therebetween being indicated by the reference numeral 42. The cross-sectional area of the evaporator at the neck or juncture 38 is indicated by the diametric line A The evaporator of FIG. 2 may be altered to provide a similar one-sided configuration having a similar vapor otftake, if desired.

As mentioned previously, the present invention also contemplates the separation of vapors and liquids by surface evaporation induced by a centrifugal force resulting from effecting a fiow of a heat saturated liquid mixture through a curved passage. This type of device may be preferred for some applicaitons of the present invention although the type of evaporator described previous- 1y is preferred for other applications because of lower friction losses.

The evaporator embodiments illustrated in FIGS. 4 to 9 are of the centrifugal type just mentioned. In these a vertical inlet conduit terminates at its lower end in a curved section which ends in a nozzle of gradually increasing cross-section. Beyond the smallest cross-section of the nozzle, or the throat thereof, are provided an outlet for the liquid and one or more outlets for separated vapors or gases. The flow of liquid in all cases, as indicated by the arrows, is downward in the inlet conduit, then through its curved section and toward the throat of the nozzle, and thence to the liquid and vapor outlets. Although the inlet conduits are shown in a vertical orientation this is for illustrative purposes alone, since the evaporators Will work in any position.

Referring now to FIG. 4, this figure illustrates an evaporator with a vertical inlet conduit 106, preferably circular in cross-section, which has an internal cross-sectional area indicated by the diametric line A Beginning at section B--B the conduit curves to the right and decreases in internal diameter to section C-C, which is at the throat of the nozzle (that curved or converging portion of the conduit between sections BB and CC is designated by reference number 107).

Beginning at section CC the conduit becomes a diverging nozzle 108 which increases in cross-section and has its largest cross-sectional area at the vertical section DD, This is the exit of the nozzle and has an internal cross-sectional area indicated by diametric line A Thus, between sections C-C and DD, the conduit forms a diverging or expanding nozzle or evaporator and separator indicated by reference number 108. This nozzle may be circular or rectangular in cross-section or have any combination of curved and/or straight walls.

Beyond and to the right of the nozzle throat at section D-D the conduit is divided into a gas or vapor take off conduit 111 in alignment with upper nozzle wall and a liquid takeoff conduit 112 diverging downwardly or outwardly therefrom. The two takeoff conduits meet at their respective inlets in a common wall 115 having an edge which faces the oncoming fluids and forms a separator between the vapor and the liquid.

In operation, using sea water as an example, heated sea water flows downwardly through the inlet conduit 106 at at a suitable temperature and velocity. During the passage of the sea water through the curved conduit portion 107 a centrifugal force is induced, varying the waters static pressure in a plane at right angles to the flow. This transverse static pressure is highest at the bottom of the curved conduit portion 107 and lowest at the top.

Starting at section CC, where the nozzle 108 begins to constrict in cross-sectional area, the static pressure on the water starts to decrease and its velocity to increase. Due to the induced centrifugal force, which varies the static pressure of the water from the top to the bottom in a plane normal to the flow directon, and the constricted cross-sectional area, which varies the static pressure in the direction of flow, and depending upon the temperature and velocity of the incoming sea water, some of the water may reach its vapor pressure shortly after entering the expanding nozzle and thus start surface evaporation at the point of lowest static pressure.

The juncture of dotted line 116 and upper wall 110 indicates the point of lowest static pressure in the liquid and the commencing of surface evaporation. As the sea water continues to progress through the nozzle and increases in velocity, its static pressure decreases further and more vaporization occurs. Dotted line 116 shows the approximate zone of separation between the vapor and the heavier liquid, the cross-sectional area occupied by While it is preferred that the curvature of the outer or bottom wall 109 of the nozzle 108 be substantially the same as that of the outer or bottom wall of the curved portion 107 of the conduit, as shown in FIG. 4, this is not essential.

the vapors increasing as the fluid passes from section C--C to the nozzle throat at section DD. The lowest static pressure occurs at the throat at section DD and it is at this point that maximum vaporization of the sea water for a particular set of conditions will be substantially completed.

As in the embodiments of the invention described previously, the diverging walls 109 and 110 confine the liquid to prevent nucleate boiling and yet permit expansion of the vapor so the evaporator will not choke. In this embodiment of the invention, as well as those described hereinafter, the turbulence necessary to maintain surface evaporation is produced by friction between the liquid and evaporator walls 109 and 110.

The separator formed at 115 by the intersection of the adjacent walls of vapor and liquid take off conduits 111 and 112 lies in the zone of separation between the vapors and the now concentrated sea water and effectively separates them so that they exit through their respective conduits 111 and 112.

FIG. shows an evaporator similar to that of FIG. 4 except for the replacement of the uniformly sectioned vapor and liquid outlets of the latter with diverging diffuser sections 119 for the vapors and 120 for the liquid being discharged from the throat of curved nozzle 121. As in the earlier described embodiment, the curved nozzle is connected at its inlet end to the lower curved portion 122 of an inlet conduit 123. The zone of separation indicated by line 124 is the same as in FIG. 4, and the common wall 125 where the diffuser sections meet separates the vapors from the concentrated sea water as in FIG. 4.

The diffusers are used to change the physical characteristics or velocities of the vapors or liquid discharged by the evaporating nozzle 121. For example, the velocity of the vapors may be reduced in the diffusing section to the point that they return to a liquid state. Such diffusers may also be used in the embodiments of FIGS. 1 to 3.

While it is apparent from FIGS. 4 and 5 that the angular extent of the angular nozzles 108 and 121 in the curved nozzle type of evaporator illustrated therein can be in the neighborhood of 50 degrees it should be understood that this angle may be larger or smaller in accordance with engineering considerations.

The various values of temperatures, velocities, pressures and other factors necessary for successful operation of the type of evaporator illustrated in FIGS. 4 and 5 may be found in or computed from conventional steam tables. The following values are given by way of example for sea water.

Steam, lbs. per hour After the surface evaporization has started at the juncture of dotted line 116 and the upper wall 110 in FIG. 4 or the corresponding point in the evaporator of FIG. 5', it is not necessary to continue the curve in the bottom wall of the evaporator. That is, the wall must continue but it can be straight instead of being curved.

The main reason why the curved wall may be dispensed with after the initiation of the surface evaporization is that, when the liquid changes into vapor through the phenomena of surface evaporation, there is a great change in density between the liquid and the vapor. This. density change necessitates a change in velocity between the liquid and the vapor. In order for this change in velocity to exist there has to be an acceleration of the vapor from the original liquid velocity. The acceleration causes a backwardly directed reaction force on the surface of the water. This reaction force replaces the induced centrifugal force existing downstream of the point just men- 8 tioned if the curve in wall 109 is maintained beyond this point.

FIGS. 6 and 7 illustrate evaporators 108a and 121a which are similar to the evaporators 108 and 121 described earlier and illustrated in FIGS. 4 and 5 except that the diverging sections have straight walls as described in the preceding paragraph. In FIGS. 6 and 7, these straight walls are identified by reference characters 109a and, 111a and 122a and 122b, respectively. In both of these figures the points at which surface evaporation is initiated and beyond which the wall curvature may be ended are the intersections of the walls with line A-A.

In the embodiment of FIG. 8 the structure is similar to that of FIG. 4 except that the curved expanding nozzle 128 has a plurality of vanes 134 and 135 in the portion through which the vapors pass to separate vapors or gases of different weights, pressures, and temperatures. The vertical inlet conduit 129 of this embodiment terminates at section E-E in a curved portion 130, which ends at section F-F at the inlet to the curved expanding nozzle (or evaporator and separator) 128. The throat of the nozzl 128 is at section FF. Dotted line 136 indicates the line of separation between the vapors and the liquid.

In operation, those liquid portions having the highest vapor pressure will vaporize first after passing the section FF where the internal diameter of the nozzle 128 begins to increas Of these vapors, and because of the temperature fall in the direction of flow, those, being the heaviest in weight, will be taken off between the innermost vane 134 and the inner or upper wall 137 of nozzle 128.

Those liquid portions having the next highest vapor pressures will be taken off between the vanes 134 and 135, and those having still lower vapor pressures will be taken'off between vane 135 and the wall 140 that separates the unvaporized liquid from the heaviest vapors with the unevaporated liquid passing through take off conduit 142.

While only two vanes 134 and 135 are shown, thus pro viding three passageways for vapor take offs, it should be understood that the number of such vanes is dependent upon the number of vapor fractions of different densities that it is desired to separate. Also, as shown in FIG. 8, the leading edges of the walls separating the various offtakes preferably terminate at the vapor-liquid separation line 136. This is most effective to separate the different vapor fractions from each other andfrom the liquid fraction exiting through take off 142.

The apparatus shown in FIG. 9 is the same as that shown in FIG. 8 except that the three take offs for the three separated vapors terminate in diffusers 145, 146, and 147 similar to the vapor diffuser 119 in FIG. 5; and the liquid take off terminates in a diffuser 150 similar to the liquid diffuser 120 of FIG. 5.

Referring now to FIGS. 10 and 11, it will be remembered that the centrifugal force required to produce a transverse pressure differential can be produced by introducing the liquid to be evaporated tangentially into the evaporator as well as by the techniques described above. The evaporator shown in the foregoing figures operates in this fashion.

In evaporator 160 hot water (or other liquid) enters the upstream end of the evaporator inlet section 162 from a pipe 164 through a tangential inlet 166. The water spirals through the gradually converging inlet section to the throat 168 of the evaporator with the spiralling of the Water being induced by the tangential entry of the water into the inlet section.

The spiralling produces a centrifugal force on the water which varies the static pressure of the water in a direction normal to the axis of the evaporator, thereby fulfilling the first of the prerequisites required for evaporators in accord with the principles of the present invention to be operable. Because of the centrifugal force the static pressure of the water is lowest in the center or on the axis of the evaporator.

Since the velocity of the water is increased due to the gradual convergence of the inlet section as it flows therethrough, the static pressure of the water is also decreased in the direction of the axis of the evaporator, fulfilling the second of the prerequisities just mentioned. At the throat of the evaporator the static pressure of the water is low enough to cause surface evaporation. This starts in the center of the liquid at evaporator throat 168 since this is the point of lowest static pressure due to the centrifugal force on the swirling water.

After the surface evaporation is started at throat 168, it continues throughout the divergent section 169 of the evaporator. The vapor from the surface evaporation forms a central core 170 which has the appearance of a right angle cone surrounded by the unevaporated water. After the proper expansion is realized the vapor and water are separated with the vapor flowing into a take off 172 of the diffuser type described above, which has an inlet 174 equal in diameter to the diameter of the vapor cone 170 at the upstream end of the take off. The liquid flows around the vapor take off into a liquid take off 176 which may be extended downwardly from the downstream end of the diverging evaporator 169 so that the force of gravity will aid in exhausting the liquid from the evaporator.

As in the embodiments of the invention described above, it is important in the surface evaporation section 169 that the included angle X between the evaporation section walls be matched with the turbulency of the water rubbing the sides of these walls since, if the angle is too large, surface evaporation will degenerate into nucleate boiling. It is also important that the converging inlet section be gradual so that a vena contracta is not formed at the throat of the evaporator. In this embodiment a vena contracta would induce a centrifugal force opposing the centrifugal force produce by the swirling liquid, defeating the effect of the latter and making the evaporator inoperable.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof such as by creating the centrifugal force required to produce a transverse pressure distribution by introducing the liquid working substance into the evaporator through spiral guides, for example. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description; and all changes which come within the mean ing and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by Letters Patent is:

1. A forced convection surface evaporator, comprising:

(a) a first conduit means for receiving heated liquid;

(b) means providing a flow restriction at the downstream end of said first conduit means, said flow restriction causing a reduction of the pressure of the heated liquid both in the direction of the flow and in a direction transverse thereto;

() means providing a divergent section bounding a space of increasing cross-section in the downstream direction, said divergent section being immediately downstream from said flow restriction, said divergent section defining the vaporization space for said heated liquid;

(d) a second conduit means extending generally in the direction of flow from the downstream end of said divergent section;

(e) a third conduit means having an inlet spaced downstream from said flow restriction, said inlet communieating with the vaporizing space bounded by said divergent section at the downstream end of said section;

(f) means for effecting a flow of heated liquid through said first conduit means and then through said flow restriction and into said divergent section and toward the inlet to said third conduit means to thereby develop a reduction of the pressure of the liquid both in the direction of flow and in a direction transverse thereto as it passes through said flow restriction and a consequent vaporization of the heated liquid in the space bounded by said divergent section and a flow of the vapor into the inlet of and through the third conduit means for removal from said space;

(g) the inlet to said second conduit means being at the downstream end of said divergent section and adjacent and communicating with the vaporization space; whereby unvaporized liquid is caused by said flow effecting means to flow into the inlet of and through said second conduit means to effect a removal of unvaporized liquid from said evaporator;

(h) said second and third conduits cooperating with said divergent section to provide a means for effecting a separation of unvaporized liquid from the vapor generated in the vaporizing space bounded by said divergent section.

2. The evaporator of claim 1, wherein said flow restriction means comprises means capable of forming a vena contracta to thereby produce a centrifugal force on the liquid.

3. The evaporator of claim 1, wherein said How restriction means comprises a convergent evaporator inlet section and said flow effecting means comprises means for introducing the liquid tangentially into the upstream end of said convergent section.

4. The evaporator of claim 1, wherein said flow restriction means comprises a convergent arcuate inlet section providing a curved flow path for said liquid and said flow effecting means comprises means for introducing the liquid into the upstream end of said inlet section.

5. The evaporator of claim 1, comprising an obstruction disposed in said divergent section of the evaporator and extending in the direction of fluid flow, said obstruction imparting turbulence to the liquid being evaporated.

6. The evaporator of claim 1, wherein said second and third conduit means have a common separating wall adjacent the outlet from said divergent section, said wall facing toward the wider portion of said divergent section and extending transversely across said divergent section in the zone where the separated vapors and liquid meet.

7. The evaporator of claim 6, Where said third conduit means comprises a plurality of vapor take offs, said take offs comprising a first vane spaced from the inner wall of said divergent section and a second vane substantially concentric with said first vane and spaced farther from the inner wall of said divergent section, and said second conduit means being on the side of said divergent section opposite said vanes.

8. The evaporator of claim 7, wherein said first vane extends a distance from the throat of said divergent section toward the wider portion thereof and said second vane extends in the same direction but not as far as said first vane.

9. A forced convection surface evaporator comprising conduit means; means for effecting a flow of hot liquid to be evaporated, said effecting means being the sole means for supplying energy to the evaporator; means restricting the conduit means; a second conduit extending linearly and coaxially with the restricting means and having its proximate open end downstream in terms of fluid flow and spaced from the restricting means; the space between the restriction and the second conduit providing an opening to a third conduit, said third conduit being directed generally in the same direction as the second conduit; means for introducing hot liquid for flow through the first conduit and thence to the restriction at a speed such that the hot liquid leaving the restriction is directed axially toward and through the second conduit developing a low pressure region adjacent to said space to vaporize a portion of the hot liquid, and thence to direct vapors so generated through the third conduit for removal of vapors from the 1 1 space, the third conduit directing the flow of vapor to form an acute angle With the flow of liquid in the second conduit; the point at which the second and third conduits intersect constituting .a means for effecting a separating of the liquid flow in the second conduit from the vapor flow in the third conduit.

References Cited UNITED STATES PATENTS 2,411,186 11/1946 Boeckeler 159-47 2,561,394 7/1951 Marshall; 2,886,297 5/1959 Crandall 259-4 FOREIGN PATENTS 259,497 10/ 1926 Great Britain.

NORMAN YUDKOFF, Primary Examiner J. SOFER, Assistant Examiner U.S. Cl. X.R. 

